Effect of foliar application of iron, zinc and manganese nano-chelate on some quantitative and qualitative characteristics of soybean (Glycine max L.) under water deficit stress

The country's food security and economy are certainly dependent on agricultural production. Today, however, water scarcity causes the agricultural product facing a serious threat. Drought stress disrupts the balance of uptake of micro nutrients and also the transfer of nutrients from roots to plant shoots. In addition, deficiency of micro nutrients can reduce the resistance of soybean to drought, as the life cycle and production of vegetable crops suffer from irreparable problems, it is therefore essential to maintain food security and provide plant protein in the human food basket. Due to the importance and role of micro nutrients in reducing the effects of drought stress, this experiment was conducted to investigate the effect of foliar application of Fe, Zn, and Mn fertilizers on soybean in irrigation interruption at different stages of plant productivity.

This experiment was conducted as split plot in a randomized complete block design with three replications on soybean cultivar M9 at Agricultural Research Farm of Islamic Azad University, Kermanshah Branch during two consecutive years (2016-2017). The climate of the area is the semi-arid cold to temperate. According to the meteorological statistics, the mean annual precipitation and temperature in the region were 480.7 mm and 15.8 °C, respectively. Fertilizer recommendation was applied on the basis of soil test results (50 kg urea and 100 kg superphosphate). Irrigation treatments were applied at four levels including complete irrigation, an interruption irrigation turn at flowering stage, podding start, seed filling period as main plots and foliar application was performed at eight levels including foliar application with Fe, Zn, Mn, Fe+Zn, Fe+Mn, Zn+Mn, Fe+Zn+Mn Nano-chelates and distilled water (control) in sub-plots. In order to foliar application of micronutrients, chemical fertilizers with the brand name of Fe (9%), Zn (12%) and Mn (12%) nano chelate in powder form that was completely soluble in water with 6.5 pH which was prepared by Khezra Company. Each experimental plot consisted of 6 rows that are 6 m length and the distance among rows was 50 cm. The seeds were impregnated with a symbiotic bacterium (Rhizobium japonicum) and were cultured manually at the depth of 5 cm and the distance of 5 cm on May 10, 2015 and 2016. Nano chelate foliar spraying was performed at a concentration of three in one thousand at two time points, stage V4 (formation of the fourth leaf on the stem) and one week after spraying the first time. The studied traits were seed yield, biomass yield, harvest index, number of pods per plant, number of pods per pod, number of seeds per plant, 1000-seed weight, oil percentage, oil yield, protein percentage and protein yield of soybean.

The results of combined analysis of variance showed that the main effects of drought stress, foliar application, and interaction between irrigation and foliar application on the studied traits was significant. The interaction of drought stress at podding stage and non-foliar application of nano chelate further reduced 1000-seed weight (30%), seed yield (34.9%), biomass yield (29.5%) and harvest index (7.6%) rather than control treatment in complete irrigation. In contrast Fe+Zn foliar application increased these traits 22.9%, 61.6% 46.5% and 10% respectively and was superior to other treatments. Oil loss percentage was more severe due to irrigation interruption at seed filling stage, and the lowest oil percentage (17.47) was obtained from combination of irrigation interruption at seed filling stage and non-foliar application and the most related to combination of complete irrigation and Zn+Mn foliar application (23.73). While the highest seed protein (39.57%) was obtained from irrigation interruption at seed filling stage and Zn+Mn foliar application. Overall, the results showed that the effect of drought stress in podding and seed filling stages on soybean yield and yield components was higher. Fe+Zn foliar application had the highest seed yield by better adjusting the stress effect. Treatments of Zn+Mn and Fe+Mn were the next priorities.

Overall, the results showed that foliar application with each of the elements Fe, Zn and Mn is an applied method to increase the micro nutrients content in plants and yield and yield components of the plant can be increased by reducing the effect of drought, under water deficit conditions, combined use of these elements was more effective. The combined treatments of complete irrigation and Zn+Mn foliar application had the highest seed yield with an average of 3704.6 kg.ha-1.